Method for producing a porous cementitious material

Abstract

The application discloses a preparation method of a silicate cement porous vegetation concrete material, and comprises the following steps: calcining coal-based kaolin to obtain activated coal-based kaolin; adding the activated coal-based kaolin and a water reducing agent into mixing water, and performing ultrasonic dispersion to form an activated coal-based kaolin suspension; weighing silicate cement, concrete recycled aggregates and fertilizer, and uniformly mixing to form dry materials; uniformly mixing the activated coal-based kaolin suspension and the dry materials, and loading into a mold for forming; and performing film covering and curing. The application is free from the low-alkalinity porous vegetation concrete system of a sulphoaluminate cement used in the preparation of a porous vegetation concrete in the prior art, and utilizes the activated coal-based kaolin after calcination and ultrasonic treatment as a main alkali-reducing agent to reduce the alkalinity of the silicate cement according to the condition that coal-based kaolin resources are rich, and the activated coal-based kaolin is matched with the fertilizer and the concrete recycled aggregates to provide a new material with rich raw material sources and low cost for ecological protection of a slope and a bank.

Description

Technical Field

[0001] This invention relates to the field of porous vegetation concrete materials technology, specifically to a method for preparing silicate cement porous vegetation concrete materials. Background Technology

[0002] Porous vegetation concrete is an eco-friendly concrete material with a continuous porous structure that supports plant growth. It is composed of cementitious materials (such as cement), coarse aggregates, appropriate amounts of fine admixtures, and additives, forming an interconnected pore system with excellent permeability and air permeability. These pores not only facilitate rainwater infiltration and reduce surface runoff but also provide growth space for plant roots and store certain amounts of water and nutrients, thus achieving an organic integration of the concrete structure and vegetation cover.

[0003] Porous vegetation concrete is widely used in slope protection, riverbank protection, urban greening, ecological restoration and other projects. While maintaining structural strength, it also has multiple functions such as ecological environmental protection, soil and water conservation and landscape beautification. It is one of the important materials in modern ecological engineering construction.

[0004] In previous studies, sulfoaluminate cement was frequently used as the low-alkalinity cement. Because the main component of sulfoaluminate cement does not generate Ca(OH)₂ during hydration, its hydration products have relatively low alkalinity, making it an ideal cement variety for preparing low-alkalinity porous vegetation concrete. However, sulfoaluminate cement is a niche product in my country, accounting for only 0.07% of total cement production. Furthermore, its raw material—high-quality bauxite (bauxite with high alumina content)—is scarce in my country, leading to a high dependence on imports and consequently, a relatively high price for sulfoaluminate cement.

[0005] For porous vegetation concrete, numerous factors influence its vegetation performance, such as the concrete's alkalinity, permeability, water absorption, and water retention. Among these, concrete alkalinity is the core influencing factor. It is well known that vegetation thrives in neutral environments. Therefore, in current research, sulfoaluminate cement, with its limited raw material reserves and low yield, but low alkalinity of its hydration products, is considered an ideal material for preparing porous vegetation concrete; while silicate cement, with its abundant raw material reserves and high yield, but high alkalinity of its hydration products, is not favored.

[0006] Kaolinite can be divided into common kaolinite and coal-associated kaolinite based on its origin. Coal-associated kaolinite, as a by-product of coal, is usually black, such as... Figure 1 As shown, it has many impurities and low kaolinite content, resulting in relatively few applications. Summary of the Invention

[0007] This invention addresses the above-mentioned problems by researching and designing a method for preparing porous silicate cement-based vegetation concrete. The technical means employed in this invention are as follows:

[0008] A method for preparing porous vegetation concrete material using silicate cement includes the following steps:

[0009] S1: Calcine coal-series kaolin at a high temperature of 600-900℃ for 1-2 hours to obtain activated coal-series kaolin;

[0010] S2: Add 2-3 parts of activated coal-series kaolin (with a mass of not less than 40% of the total mass of silicate cement and activated coal-series kaolin) and 4000 parts of mixing water to ultrasonically disperse the mixture to form an activated coal-series kaolin suspension, thereby further enhancing its activity.

[0011] S3: Weigh 500-600 parts of silicate cement, 8000-9000 parts of recycled concrete aggregate, and 10-50 parts of fertilizer, mix them evenly to form dry material;

[0012] S4: Mix the activated coal-series kaolin suspension with the dry material evenly and then fill the mold to form the product.

[0013] S5: Covering and curing to form a low-alkalinity silicate cement porous vegetation concrete material.

[0014] The number of parts mentioned in this invention refers to parts by weight.

[0015] As a preferred embodiment, the weight ratio of coal-derived kaolin to silicate cement is 4:(5-6), and the fertilizer includes one or more of urea, superphosphate, and potassium chloride.

[0016] As a preferred embodiment, the recycled concrete aggregate is 18-20 mm single-grade recycled concrete aggregate, and the water-reducing agent is a polycarboxylate water-reducing agent.

[0017] As a preferred option, in step S4, after inserting the template, compact it for 1-2 minutes under a pressure of 30-40 kPa; in step S5, the curing time is more than 14 days.

[0018] Compared with existing technologies, the method for preparing porous vegetation concrete material using silicate cement described in this invention departs from the low-alkalinity porous vegetation concrete system using sulfoaluminate cement previously employed. Leveraging the abundant coal-bearing kaolin resources in Inner Mongolia, Shanxi, and Shaanxi, this method utilizes activated coal-bearing kaolin, after calcination and ultrasonic treatment, as the main alkali-reducing agent to lower the alkalinity of silicate cement to an extremely low level. Combined with fertilizers and recycled concrete aggregates, this method prepares a silicate-based fertilizer composite recycled aggregate porous vegetation concrete slope protection material that possesses both mechanical properties and ecological functions. This provides a new material with abundant raw material sources and low cost for the ecological protection of slopes and embankments. Attached Figure Description

[0019] Figure 1 a and b are examples of photographs of ordinary kaolinite and coal-bearing kaolinite, respectively.

[0020] Figure 2 This is the X-ray diffraction pattern of activated coal-series kaolinite as described in the embodiments of the present invention.

[0021] Figure 3 a and b are the microscopic morphologies of the calcined coal-series kaolin before and after ultrasonic dispersion, respectively, under a transmission electron microscope in the embodiments of the present invention.

[0022] Figure 4 The compressive strength of coal-series kaolin before and after ultrasonic dispersion in the embodiments of the present invention is shown.

[0023] Figure 5 This is a graph showing the Ca(OH)2 content in porous vegetation concrete with different activated coal-series kaolin content in embodiments of the present invention (through thermogravimetric analysis).

[0024] Figure 6 The content of Ca(OH)2 in porous vegetation concrete with different activated coal-series kaolin content in the embodiments of the present invention (by X-ray diffraction test).

[0025] Figure 7 This refers to the alkalinity (phenolphthalein impregnation method) of low-alkalinity silicate cement porous vegetation concrete with different activated coal-series kaolin content in the embodiments of the present invention.

[0026] Figure 8 This invention relates to the alkalinity changes of low-alkalinity silicate cement porous vegetation concrete under different fertilizer dosages during the 28-day curing process (phenolphthalein impregnation method). Detailed Implementation

[0027] A method for preparing porous vegetation concrete material using silicate cement includes the following steps: The preparation method of porous vegetation concrete includes the following steps: (1) calcining coal-based kaolin at a high temperature of 800 ℃ for 2 h; (2) weighing calcined coal-based kaolin and an appropriate amount of polycarboxylate superplasticizer, which are not less than 40% of the total mass of silicate cement and activated coal-based kaolin, and adding them to the mixing water, and using ultrasonic dispersion to reduce the agglomeration of calcined coal-based kaolin to further improve its activity; (3) weighing silicate cement, single-grade concrete recycled aggregate, fertilizer (urea, superphosphate and potassium chloride) and other dry materials, and putting them into a mixer to mix evenly; (4) then adding ultrasonically dispersed activated coal-based kaolin suspension to the dry materials and continuing to stir; (5) After the cementitious material evenly covers the surface of the recycled concrete aggregate, it is quickly discharged and spread and leveled in the template. It is compacted by low-frequency vibration or light pressing to avoid the pores being compacted and closed. For example, it is compacted for 1-2 minutes under a pressure of 30-40 kPa. After molding, it is promptly covered with a film for curing to prevent the moisture from evaporating too quickly. The curing time is generally not less than 14 days. (6) After curing, planting soil or grass seeds can be laid on its surface to achieve vegetation growth and finally form a porous vegetation concrete system with both mechanical properties and ecological functions.

[0028] like Figure 2 As shown, the X-ray diffraction peaks of the calcined and activated coal-based kaolin are diffuse, indicating a transitional phase with poor crystallinity, suggesting that the calcined coal-based kaolin possesses certain potential pozzolanic activity.

[0029] like Figure 3 As shown, calcined coal-based kaolin transformed from an aggregated state to a dispersed state after ultrasonic activation. The ultrasonic treatment increased the contact area between the calcined kaolin and cement, simultaneously increasing the number of nucleation sites in the cement and improving its hydration level. Therefore, the activity of the calcined coal-based kaolin increased.

[0030] like Figure 4 As shown, compared to cement paste prepared from calcined coal-based metakaolin without ultrasonic activation, cement paste prepared from calcined coal-based metakaolin with ultrasonic activation exhibits a compressive strength increase of approximately 19.4%. This is consistent with... Figure 3 The results are consistent with those of the dispersion state test of calcined kaolin.

[0031] like Figure 5 As shown, Ca(OH)₂ is the main hydration product of silicate cement, accounting for approximately 20% of the total mass of hydration products. Ca(OH)₂ is also the main reason why concrete can maintain a high alkalinity. Figure 3It can be seen that when the activated coal-bearing kaolin reaches about 40%, the Ca(OH)2 content in the porous vegetation concrete has decreased to a level that is difficult to detect by thermogravimetric analysis. This indicates that the alkalinity of the porous vegetation concrete has decreased to a very low level at this point, which is consistent with... Figure 6 The results were consistent with those of the phenolphthalein infiltration test.

[0032] like Figure 6 As shown, when the activated coal-series kaolin content exceeds about 40%, the Ca(OH)2 content in the porous vegetation concrete has decreased to a level that is difficult to detect by X-ray diffraction experiments, indicating that the alkalinity of the porous vegetation concrete has decreased to a very low level at this time.

[0033] like Figure 7 As shown, when the activated coal-series kaolin content reaches 40%, the alkalinity of the recycled aggregate concrete has decreased to a level where phenolphthalein cannot detect it (phenolphthalein is known to be colorless at pH < 8.2). This indicates that the alkalinity of the concrete has decreased to an extremely low level, and this near-neutral environment is very conducive to vegetation growth. This is consistent with thermogravimetric analysis (TGA). Figure 4 ) and XRD test ( Figure 5 The test results were consistent.

[0034] like Figure 8 As shown, the rate of alkalinity decrease in cement stone after adding fertilizer is slower, and the higher the dosage, the slower the decrease. However, after 28 days of curing, the alkalinity of all fertilizer-added cement stone can decrease to a level where phenolphthalein cannot detect it (phenolphthalein is known to be colorless at pH < 8.2). When the dosage of activated coal-series kaolin reaches 40%, the alkalinity of recycled aggregate concrete has decreased to a level where phenolphthalein cannot detect it (phenolphthalein is known to be colorless at pH < 8.2), indicating that the alkalinity of cement stone can also be reduced to an extremely low level after adding fertilizer.

[0035] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing a porous portland cement concrete material for vegetation, characterized by, Includes the following steps: S1: Calcine coal-series kaolin at a high temperature of 600-900℃ for 1-2 hours to obtain activated coal-series kaolin; S2: Add 2-3 parts of activated coal-series kaolin (with a mass not less than 40% of the total mass of silicate cement and activated coal-series kaolin) and 4000 parts of mixing water, and disperse them by ultrasonication to form an activated coal-series kaolin suspension. S3: Weigh 500-600 parts of silicate cement, 8000-9000 parts of recycled concrete aggregate, and 10-50 parts of fertilizer, mix them evenly to form dry material; S4: Mix the activated coal-series kaolin suspension with the dry material evenly and then fill the mold to form the product. S5: Covering and curing to form a porous silicate cement-vegetated concrete material.

2. The method of claim 1, wherein the portland cement porous vegetation concrete material is prepared by mixing the portland cement, the aggregate, the water, and the additive. The weight ratio of coal-series kaolin to silicate cement is 4:(5-6), and the fertilizer includes one or more of urea, superphosphate and potassium chloride.

3. The method of claim 1, wherein the portland cement porous vegetation concrete material is prepared by mixing the portland cement, the aggregate, the water, and the additive. The recycled concrete aggregate is a 18-20 mm single-grade recycled concrete aggregate, and the water-reducing agent is a polycarboxylate water-reducing agent.

4. The method of claim 1, wherein the portland cement porous vegetation concrete material is prepared by mixing the portland cement, the aggregate, the water, and the additive. In step S4, after inserting the template, compact it for 1-2 minutes under a pressure of 30-40 kPa; in step S5, the curing time is more than 14 days.

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